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In February 2003 Andrea Arcangeli put forward his idea for a Stochastic Fair Queueing I/O scheduler to Jens Axboe who then implemented it. Jens Axboe made improvements to his first implementation, calling the new version the Completely Fair Queueing scheduler, and produced a patch to apply it to the 2.5.60 development series kernel.
In contrast to the previous O(1) scheduler used in older Linux 2.6 kernels, which maintained and switched run queues of active and expired tasks, the CFS scheduler implementation is based on per-CPU run queues, whose nodes are time-ordered schedulable entities that are kept sorted by red–black trees. The CFS does away with the old notion of ...
For example, if a modem expansion card is added into a system and assigned to IRQ4, which is traditionally assigned to the serial port 1, it will likely cause an IRQ conflict. Initially, IRQ 7 was a common choice for the use of a sound card , but later IRQ 5 was used when it was found that IRQ 7 would interfere with the printer port ( LPT1 ).
The Linux kernel's packet scheduler is part of the network stack, together with netfilter, nftables, and Berkeley Packet Filter. The Linux kernel packet scheduler is an integral part of the Linux kernel's network stack and manages the transmit and receive ring buffers of all NICs.
MSI increases the number of interrupts that are possible. While conventional PCI was limited to four interrupts per card (and, because they were shared among all cards, most are using only one), message signalled interrupts allow dozens of interrupts per card, when that is useful. [1] There is also a slight performance advantage.
Fair queuing uses one queue per packet flow and services them in rotation, such that each flow can "obtain an equal fraction of the resources". [1] [2]The advantage over conventional first in first out (FIFO) or priority queuing is that a high-data-rate flow, consisting of large packets or many data packets, cannot take more than its fair share of the link capacity.
Read queues are given a higher priority because processes usually block read operations. Next, Deadline checks if the first request in the deadline queue has expired. Otherwise, the scheduler serves a batch of requests from the sorted queue. In both cases, the scheduler also serves a batch of requests following the chosen request in the sorted ...
A proposed workaround is for the operating system to artificially starve the NCQ queue sooner in order to satisfy low-latency applications in a timely manner. [ 10 ] On some drives' firmware, such as the WD Raptor circa 2007, read-ahead is disabled when NCQ is enabled, resulting in slower sequential performance.